Manifold Vacuum Advance what am I not getting?

Oh and one thing I've noticed while messin around with mine is worth sharing. These vacuum caps that these parts stores sell now don't last ANY time before they crack, split and LEAK, so keep an eye out for that! I don't know where a good source for vacuum caps is. What a stupid problem to have!
Get silicone caps and plugs for powder coating masking. Made to take high heat.